Energy and CO2 usage in the UK is currently calculated using one of four standard energy models: Standard Assessment Procedure 2005 (SAP 2005), Reduced Standard Assessment Procedure (RdSAP), National Home Energy Rating (NHER) and Simplified Building Energy Model (SBEM). These rely on theoretical data produced from building plans and on site observations. Typical data recorded is wall construction, heating system, floor area, building location etc. Output from these models details the estimated energy consumption from the property, associated costs and the CO2 emissions.
SAP 2005 has been used as the basis for checking new dwellings for compliance with building regulations in the United Kingdom requiring the conservation of fuel and power since 6 Apr. 2006 (England & Wales: L1 Approved Document), 1 Nov. 2006 (Northern Ireland Technical Booklet F1) and 1 May 2007 (Scotland Technical Handbook 6, Domestic). New legislation within the UK, the Energy Performance Directive of Buildings Directive (EPBD) and the Home Information Pack (HIPs), states that every UK property should be assessed for energy efficiency and an energy rating derived for each property. This calculation is to be based on the RdSAP assessment model.
A limitation of these known assessment models is that they assume buildings have been built 100% to specification with 100% accuracy. No allowance is made for any building defects where the builder's accuracy has been lacking, such as gaps in insulation or poorly fitting details. Currently, the only way to assess a building for its ‘quality’ of build is via an Air Leakage/Permeability Test, intrusive/destructive testing via boroscopic evaluation or heat flux tests through the structure. The Air Permeability Test is a constituent of Part L: conservation of Fuel in England and Wales and Part J of the building regulations within Scotland. This test, however, provides a pass/fail certificate and does not show the areas of air loss. This can be overcome by using smoke generators within the property. However, this only lasts a short time and does not highlight areas responsible for the highest air leakage, nor can it highlight areas of missing insulation within the structure.